Currently, there are a wide variety of known chromogenic materials that can provide optical switching in thin film form. These materials and their applications have been reviewed recently by C. B. Greenberg in Thin Solid Films, Vol. 251, pp. 81-93 (1994); R. J. Mortimer in Chemical Society Reviews, Vol. 26, pp. 147-156 (1997); and S. A. Agnihotry in Bulletin of Electrochemistry, Vol. 12, pp. 707-712 (1996).
Such chromogenic materials are currently being studied for several applications, including active darkening of sunglasses, active darkening of windows for intelligent light and thermal management of buildings, and various types of optical displays (such as heads-up displays on the inside of windshields of automobiles or airplanes and eyeglass displays). Despite their long history of great promise, there are very few photon gating devices made from the existing classes of electrochromic materials. This is because most of them require an oxidation-reduction reaction that involves the transport of ions, such as H+, Li+ or Na+, through some type of liquid or solid electrolyte. Finding the appropriate electrolyte is a major problem, as is the slow speed of any device that requires transport of ions. Furthermore, such reactions are extremely sensitive to background contamination, such as oxygen and other species, and thus degradation of the chromogenic electrodes is a major limitation.
In fact, for photonic switching applications such as a crossbar switch router for a fiber optic communications network, the lack of a suitable chromogenic material has forced companies to use very different approaches: (a) transform the optical signal into an electronic signal, perform the switching operation, and then transform back to an optical signal before launching into a fiber—this is the most frequent solution used today but it is very inefficient and the electronics have a hard time keeping up with the data rates of the optical system; (b) use a moving-mirror array made by micro-electromechanical processing to switch optical data packets—this has the disadvantage that extremely high tolerances are required for the device, which makes it very expensive, and (c) use ink jet technology to push bubbles into a chamber to create a mirror to deflect an optical beam—this approach again requires precision manufacturing and the switching time is slow.
Thus, there remains a need for an optical switch that can rapidly switch optical signals from one path to another with low power dissipation.